Markdown output

plan --output markdown prints the plan as a comment to post on a pull request, so the plan can be reviewed before merging:

gh infra plan ./repos/ --output markdown > plan.md

Like JSON output, stdout has only the comment, and the exit status is the same as with text output. It is built from the same data as JSON output.

The comment starts with the summary, then has one collapsed block per repository with a table of its changes. Grouped settings are shown one row per setting (features.wiki). With --diff, each file change gets its own collapsed block with the diff. Warnings and errors come last; if some repositories could not be planned, the comment says the plan is incomplete.

### Plan: 1 to create, 2 to update, 0 to destroy

<details><summary><code>babarot/my-cli</code>: 1 to create, 2 to update</summary>

| | Resource | Name | Change | Before | After |
|---|---|---|---|---|---|
| ~ | Repository |  | <code>description</code> | <code>old</code> | <code>new</code> |
| ~ | Repository |  | <code>features.wiki</code> | <code>false</code> | <code>true</code> |
| + | Label | <code>bug</code> |  |  | <code>#d73a4a</code> |

</details>

With --changed-since, the summary is followed by Planned N of M resources changed since <ref>., and when nothing changed the heading is ### Plan: no manifests changed since <ref> instead of ### Plan: no changes, so the comment shows whether anything was planned.

Values are cut at 200 characters, and diffs at 500 lines per file. The comment is not otherwise limited in size, so a very large plan can go over GitHub’s limit of 65,536 characters per comment.

Posting it from GitHub Actions

The Plan on pull request workflow posts this comment on every pull request: it plans only what the pull request changed, keeps one comment per pull request with gh pr comment --edit-last --create-if-none, and fails the check only when the plan itself fails. The job needs pull-requests: write.

With --detailed-exitcode, plan exits with 2 when there are changes, which fails the step; capture the exit status as that workflow does, so the comment is still posted.